1. October 2002J. B. Wordsworth: J2ISDPPC1 Information Systems Development Problem Frames: Problems and Contexts

2. October 2002J. B. Wordsworth: J2ISDPPC2 Problems There are many kinds of problem for which a computer- based solution is required. There are many different methods of creating computer- based solutions. Problems can be classified, and analysed into interacting subproblems. A problem frame is a class of similar problems, with similar solutions.

3. October 2002J. B. Wordsworth: J2ISDPPC3 Domain A domain is a coherent set of real-world phenomena. There are always at least two domains: the machine domain (which is to be constructed in the solution) and the application domain (which is the part of the real world that the machine domain is to serve). The application domain must often be analysed into several other domains. Domains have interfaces that consist of shared phenomena.

4. October 2002J. B. Wordsworth: J2ISDPPC4 A context diagram Periods and ranges Medical staff Monitor machine Nurses’ station Analog devices ICU patients (from Jackson's Problem Frames)

5. October 2002J. B. Wordsworth: J2ISDPPC5 Domain types Machine domain: to be constructed. Designed domain: to be constructed. Can it be absorbed into the machine domain? Given domain: to be investigated.

6. October 2002J. B. Wordsworth: J2ISDPPC6 What about the database? Is it a helpful suggestion about an implementation?, then it shouldn't be here. Is it predefined, to be shared by other applications?, then it is a given domain. Is it a designed domain to be used by other applications?, then we must include the other applications in the context.

7. October 2002J. B. Wordsworth: J2ISDPPC7 Domain interfaces Periods and ranges Medical staff Monitor machine Nurses’ station Analog devices ICU patients (from Jackson's Problem Frames) a b c e f

8. October 2002J. B. Wordsworth: J2ISDPPC8 Shared phenomena Domains communicate by shared phenomena. For each interface, the shared phenomena must be investigated, named, and described. a: Period, Range, PatientName, Factor b: EnterPeriod, EnterRange, EnterPatientName, EnterFactor c: Notify e: RegisterValue f: FactorEvidence

9. October 2002J. B. Wordsworth: J2ISDPPC9 Connection domains A connection domain connects two other domains. Can be liable to erroneous removal by abstraction. Connection domains are required if: connections are unreliable connections introduce delays that are an essential part of the problem connections convert phenomena connections are in the requirements

10. October 2002J. B. Wordsworth: J2ISDPPC10 Large contexts In large contexts there might be too many domains. Consider aggregating several small problem domains into one large domain. Draw a context diagram for each of the large domains, showing how it is composed of smaller domains.

11. October 2002J. B. Wordsworth: J2ISDPPC11 Machines and domains Every machine domain is a computer. Sometimes a computer can be a given domain. Sometimes the same computer can be both!

12. October 2002J. B. Wordsworth: J2ISDPPC12 Summary Context diagrams identify the problem domains and limit the scope of the problem. A domain can be a machine domain, a designed domain or a given domain. Domains communicate by sharing phenomena: the context diagram is annotated to show the shared phenomena. Connection domains are in danger of being removed by excessive abstraction.